1. Field of the Invention
This invention relates to methods of forming rim type attenuating phase shifting masks using a single layer of resist material and a single resist developing solution.
2. Description of the Prior Art
Patent Application TSMC-97-077, Ser. No. 08/957,676, filed Oct. 24, 1977, entitled "A NEW MASK AND METHOD TO ELIMINATE SIDE-LOBE EFFECTS IN ATTENUATED PHASE SHIFTING MASKS," and assigned to the same assignee describes the use of rim type attenuating phase shifting masks.
A paper entitled "Primary Process in E-Beam and Laser Lithographies for Phase-Shift Mask Manufacturing" by Yoichi Takahashi et al., SPIE Vol. 1674 Optical/Laser Microlithography V, 1992, pages 216-229 describes a comparison of using a LASER writer as opposed to an electron beam writer in the fabrication of phase shifting masks.
"ULSI Technology," by C. Y. Chang and S. M. Sze, McGraw-Hill, 1996, pages 284-289 describes making rim type phase shifting masks using electron beam direct writing, two layers of resist, and two developing steps.
"ULSI Technology," by C. Y. Chang and S. M. Sze, McGraw-Hill, 1996, pages 311-312 describes a double exposure of two layers of resist with different sensitivities. The top layer of resist has a higher sensitivity than the lower layer of resist. The top layer of resist is first exposed and developed followed by exposure and developing of the second layer of resist.
U.S. Pat. No. 5,620,817 to Hsu et al. describes a method of forming a rim type attenuating phase shifting mask by exposing a layer of negative photoresist through the back surface of a transparent mask substrate using a patterned layer of attenuating phase shifting material as a mask. The exposed and developed photoresist forms pedestals with sloping sides. Opaque material is then deposited using the pedestal overhang to form a rim type mask.
U.S. Pat. No. 5,532,089 to Adair et al. and U.S. Pat. No. 5,384,219 to Dao et al. describe methods of forming a phase shifting mask which differ from the method of this invention.
U.S. Pat. No. 5,244,759 to Pierrat describes a method of forming a phase shifting mask using a single resist layer using two exposure doses and two developing steps. After the two exposure doses the resist layer is developed a first time in a first developing solution and used for etching part of the mask. The resist layer is then developed a second time in a second developing solution and used for further etching of the mask. In this method two developing steps in two different developing solutions are required.
U.S. Pat. No. 5,582,939 to Pierrat describes a method of avoiding defects in forming phase shifting masks using an etch stop layer, a phase shifting layer, and an opaque layer.
U.S. Pat. No. 5,472,813 to Nakagawa et al. describes a pattern exposing method to form a predetermined resist pattern on a substrate using a first resist layer and a second resist layer.
U.S. Pat. No. 5,460,908 to Reinberg describes a method of forming a phase shifting reticle that can be used as a mask.
"Handbook of Microlithography, Micromachining, and Microfabrication," Volume 1: Microlithography, P. Rai-Choudhury, Editor, SPIE Optical Engineering Press, 1997, pages 435-437 describes process sequencing for masks patterned using electron-beam and LASER based exposure sources.
This invention describes methods of forming rim type attenuating phase shifting masks using a single resist layer and a single developing solution.